A Content Delivery Network (CDN) is a globally distributed network of servers — called edge nodes or Points of Presence (PoPs) — that cache and serve web content from locations close to end users. When a user in London requests a page from a US-hosted website, the CDN serves the response from a London edge server rather than routing all the way to the origin, dramatically reducing latency and load on the origin server.
For web scraping, CDNs are significant because the most widely deployed anti-bot protections (Cloudflare, Akamai, Fastly, Imperva) operate at the CDN edge — they intercept every request before it reaches the origin server. TLS termination, fingerprinting, bot scoring, and challenge serving all happen at the edge node closest to the scraper's proxy IP.
Geographic proximity affects scraping performance in two ways: CDN edge selection (a proxy IP in Europe hits a European edge, which may have different caching behaviour than the US edge) and origin round-trip (for cache misses, all edges must still contact the origin, adding latency). Understanding that anti-bot is deployed at the CDN layer explains why changing the target IP or port does not bypass the protection.